A quick flash of light can make ordinary materials extraordinary, potentially inducing qualities such as the perfect efficiency of superconductivity even at room temperature. But these subatomic transformations are infamously fleeting--they vanish in just trillionths of a second.

An international team of scientists, including researchers from Institute of Physics of Chinese Academy of Sciences, the U.S., Germany, Japan, Spain, and the UK, has used synchronized infrared and x-ray laser pulses to simultaneously manipulate and reveal the ultra-fast magnetic properties of this promising quantum landscape. The rapid, light-driven switching between magnetic states, explored here with unprecedented precision, could one day revolutionize the reading and writing of data in computers and other digital devices.

Nowadays, large X-ray free electron laser (FEL) facilities, such as Linac Coherent Light Source (LCLS) and SPring-8 Angstrom Compact Free Electron Laser (SACLA), can supply high quality x-ray pulses with remarkable short time length of femtoseconds. The challenge is how to use such powerful tool to detect the dynamic response of the spins. That is, a specialized x-ray detection system or 'camera' is needed. The scientists developed a highly specialized resonant inelastic X-ray scattering (RIXS) spectrometer for FEL, which used millimeter-sized silicon crystals to measure the exact energy of the rebounding x-rays, allowing reduction of the transient electronic and magnetic qualities.

In this work, the scientists used a strontium-iridium-oxygen compound (Sr₂IrO₄), selected for its strong magnetic interactions. An infrared laser was used to manipulate the spin, and time-resolved RIXS (tr-RIXS) was used to catch the spin in motion. The data revealed a clear difference in the propagation and timescale of the magnetic phenomena, with the inter-layer correlations taking hundreds of times longer to recover than those within each layer. More importantly, the magnetic dynamics showed significant difference between the equilibrium state and the transient state, where the low energy magnon spectral weight was largely enhanced. This indicates that the low energy spin dynamics is strongly coupled to the carriers, which come from photo-doping in this case.

These findings demonstrate the strength and precision of tr-RIXS, which opens the door to reveal femtosecond magnetic dynamics in as yet unseen detail. It made one more step closer to perfecting a recipe for manipulating materials on ultra-fast time scales.

This study entitled "Ultrafast energy- and momentum-resolved dynamics of magnetic correlations in the photo-doped Mott insulator Sr₂IrO₄" was published in Nature Materials.

The study was supported by the National Science Foundation, the Ministry of Science and Technology of China, the Chinese Academy of Sciences and also grants from the U.S., Germany, Japan, Spain, and the UK.